Thermostat



B. J. PEPPER Dec. 9, 1930.

THERMOS TAT mm f lllllllllllll.;

Dec. 9, 1930.

B. J. PEPPER THERMOSTAT Filed Jan- 30. 1925 2 Sheets-Sheet 2 frufenc.

ron J P6] el Patented Dec. 9, 1930 PATENT 0FFICE- BYRON J. PEPPER, or:Foam WAYNE, INDIANA THERMOSTAT Application led January My inventionrelates to the art'of temperature control and more specifically to athermostatic control system of which I have illustrated an embodimentparticularly adapted '5 for precise automatic control of the heattreatment or pasteurizing of milk.

en an ordinary thermometer bulb, comprising a container filled with aliquid of diiierent expansivity than itself, is exposed to changes intemperature, the initial incidence of any change on the bulb will changethe temperature of the bulb before it can possibly change thetemperature of its contents.

This will 'produce an initial change in the indication precisely theopposite of the temperature change to which the bulb is being subjected.Where the thermometer is only being used to indicate the finaltemperature after prolonged immersion, this is immaterial, but where theresponse of the thermometer exerts a constant control on a supply oftemperature changin medium for the purpose of controlling an stabilizingthe temperature of material under treatment, this initial response inthe wrong direction will momentarily exert a control in the wrongdirection so that the system is unstable, i. e., any initialdisplacement from an equilibrium position tends automatically to resultin further displacement in the same direction. Such a system can, andordinarily will, oscillate continuously above and below a certain meanvalue.' This phenomenon may be referred to in general as hunting.

Among the functional objects and advantages of the invention may beenumerated:

' First. The provision of a thermometer element with an initial responsein the same direction as the momentary temperature change, resulting ina. system that will not hunt and that will be dead beat in the sense fthat it will-come to equilibrium from a condition not in equilibrium,without any inal oscillation. A

Second. To secure an initial response not only in the right directionbut much more prompt and rapid, especially at first.

Third. To secure uniformity in response, especially-in the sense thatthe responseto any giventemperature change is substantial- 30, 1925.Serial No. 5,754.

ly independent of the history of the system.

Fourth. To secure a yfairiiieasure of calibration and calibratedadjustment. In the embodiment disclosed vthis involves an adjustment soas to maintain an at least approximately uniform and linear relationbetween the disturbance and the response of the control system thereto.

Among the structural advantages of the invention, may be enumerated:

First. The compactness of the resulting structure due largely to thedouble function previous temperature performed by the tubularthermometer bulb,

which functlons as a conduit.

Second. A reduction in the necessary size of' the parts incidentprimarily to the principle embodied in obtaining the fourth functionalobject above mentioned.

rIhird. A practical adjustment indicator for convenience in controllingthe system.

In the accompanying drawings, showing one of the many and variedapplications of the device: j

Fig. 1 is a side elevation of the thermostat control parts complete witha diagrammatlc indication of a heat treating device controlled thereby.

Fig. 2 is a central longitudinal section of the control valve for thetemperature changing medium. A

Fig. 3 is a plan view', and Fig. 4 a centra longitudinal section of thethermometer bulb.

Fig. 5 is an enlarged detail of the joint at the end of the bulb.

In the embodiment of the invention selected for illustration, the systemunder control has been indicated diagrammatically as a container 10filled With'the liquid 12 to be'treated, which liquid may enter throughany suitable inlet device 14. Container 10 isy jacketed with a largercontainer 16, the temperature changing element beingdelivered to thejacket throu h an inlet pipe 18 and leaving the same t rough an .exhaustpipe 20. Assume, for.the purpose of illustration, that the liquid 12 ismilk and the jacket is filled with water heated by steam injectedthrough pipe 18, the increase in volume due to condensation of the steambeing relieved through pipe 20. The liquid leaves container l() througha tubular structure indicated as a whole by thereference 5 character 22,provided with a T connection 24 for convenience in delivering the liquidpassing through the device at any time Ito veither of the two differentreceiving means. The branch connection would be useful, for instance, ifsteam or hot water were being passed through container to clean orsterilize it. Itis also required by statute in many places for sanitaryreasons.

According to the invention the thermometer bulb comprises a thin annularchamber 26 built into, and forming part of, the tubular structure 22. I`have illustrated an outer tube 28 of steel, heavily nickel plated, asindicated at 30, and an inner tube 32, preferably of bare copper. Thesemay be encircled first by a retaining collar 34 having an anj nularshoulder to engage the clamping 'union 36 provided with turning pins 38,and second, by a tubular member 40 defining a discharge chamber 42communicating with the 'bulb through an aperture at 44, and a calibration and adjustment chamber at 46 having similar communication throughorifices at 48. T 24 is suitably connected to the delivery end of thestructure as by sweating it on the outer end of the tube 28 at 50. Inthe embodiment shown, collar 34 has been placed intermediate the ends ofthe bulb to shorten the distance from the tank to the discharge 35 T.Where such compactness is not essential it would obviously be placed atthe extreme end of the bulb.

Cross rings 52 at the ends of chamber 26 are integrally united with theinner and outer tubes 32 and 28 to hermetically seal the chamber.'Chamber 46 contains an adjustable displacement unit in the form of acollapsible metallic bellows 54 attached at its upper end to the crosscap 56 and at its lower end to the end plate 58 carried by a stem 60shouldered at 62 andextending through cap 56 for threaded connectionwith an adjustable nut 64 resting on top of the cap and held 1n place bya spring 66 entering corrugations 68 at its periphery. The threadedportion of Y the stem is flattened on one side 'at 69, the

dat portion terminating in a lshoulder for a purpose to be explainedhereinafter.

In some instances it is desirable to shorten 55`the length of astructure including the ther- 60 stat at 73 and compel the same to moveto 'the left outside the tube and back tothe rightrinsde the same.

It will be apparentthat the initial response of the thermometer bulbshown will be pro- 465 duced when the tube 72is omitted by the hot orcold liquid impinging in the first instance on the copper tube 32. Theresultant expansion or contraction of this tube will force some of thecontents ofthe chamber out or draw it into the chamber from the chamber42, and-the subsequent transfer of the new temperature condition to theliquid in the bulb will result in continued displacement in the samedirection. It will be apparent that ifv the temperature change wereeffective first on tube 28 only, the above bulb would have all thedefects of the ordinary bulbs of the prior art. To eliminate this andstill permit the use of tube 72, I form tube 28 of heavily nickel platedsteel whereby it constitutes a thermal barrier between the contents ofthe bulb and the liquid outside several timesmore effective than tube32. ,This difference in conductivity combined with the lower expansivityof the outer tube results in such a time-lag in the effectiveness of theexpansion or contraction of tube 28 that under all normal conditions ofuse the change in temperature reaches the tube 32 at leastsimultaneously with the effect on tube 28, so as to more than neutralizeit.

The flow control means I have illustrated comprises a valve casing 74having an outlet chamber 75 and a double inlet chamber 76 lying on bothsides thereof. Valve 78 has an upper plate at 80 co-operating with theupper cylindrical seat 82 and a lower plate at 84 co-operating with thelower c lindrical seat 86 so that 1t is balanced 'an u naffected by theflow of fluid through the same. The valve is normally held up against astop 88 by means of spring 90 housed in cap 92 and guided on suitablepins 94. Stop 88 is continued in the form of a central rod extending up'to the upper head 96 of the collapsible metallic bel ows 98 housel inchamber 100. That portion without the bellows -being hermetically sealedfrom the portion inside and constituting an expansion chamber in whichthe displacement of rod is varied by expansion of liquid in chamber 100and connectin chambers. A suitable small connecting 'tu 102 connectschamber 100 with the thermometer bulb.

The whole systemis filled with a suitable liquid of proper expansivity.The lighter mineral hydrocarbon oils are suitable-'but .viousadjustmentundisturbed. Chamber 46 is of sufficiently large capacity to care forany abnormal expansion, such as that occurring when a control adjustedfor pasteurizing milk is sterilized with live steam. Under suchcircumstances, valve 77 will first close completely against the actionof spring 90 until the stop point 91 on the poppet 78 comes into contactwith the end of stop 94 on cap 92. This prevents the abnormal expansionfrom injuring bellows 98. Further expansion of the liquid in the systemwill lift plate 58 toward cap 56, compressing bellows 54 and spring 66and lifting nut/64 oii'f of cap 56. The stop spring or clip 66 is ofsucient length to remain engaged with its corrugation 68 and form aguide so that when contraction of the liquid takes place as theapparatus cools, the adjustment for thermostatic operation will remainas before and need not be made over again. The shoulder 62 on the stem60 is far enough from cap 56 to permit any abnormal expansion of thisnature. v

It is a well known fact that the 'flow of a compressible Huid through anorifice with fixed pressures on both sides of the orifice is a linearfunction of the area of the orilice, but where the nal pressure is morethan approximately fifty-'eight one-hundredths of the initial pressure,any change in pressures eiects a' large change in the constant ofproportionality between area and flow. In a system controlled by such lavalve as that shown lin Fig. 2 operating with a drop in pressure throughthe valve less than that necessary to eliminate the eiect of the finalpressure, the ow as a function of the axial displacement of the valve isrepresented by a curve of large curvature, having .a relatively straightportion at one end. y.By cutting down on the valve opening for normalad-v justment to a point where the iiow is independent of the finalpressure` operation can be had over a range where the rate of liow issubstantially a linearfunction of the displacement'of rod 88. l Thisproduces two very important results. First, 'the linear relationshipobtained makes it possible to adjust plunger 60 and calibrate theadjustment with fair precision over a considerable temperature range.Thus a machine may be initially constructed so that with the notch 7 0flush with the surface of adjusting nut 64, a temperature of say 140Fahrenheit will be maintained in the machine, and rotation of the nut ineither direction will change the temperature up or down by amountssubstantially directly proportioned to the extent of change inadjustment. Notch 70 is convenient to keep track of the number of turns,or to provide an indication in case the adjust# ing nut may have beeninadvertently turned since a previous operation and should be adjustedbefore starting another run.` The second advantage is that theconsiderable decrease in the displacements ofl the valve, necessary toproduce adequate variations in flow, correspondingly. reduces the sizeof the thermometer bulb required and the 'size of the metallic bellows98 and its housmg.

In constructing a system to operate according to the method aboveoutlined I proceed by choosing valve and pipeconnections of suliicientlylar e calibre so that flow of the temperature c anging iuid is in no waylimited at the maximum demand by the pipe connections and valve passagesthemselves. I then elongate stem 87 so that it will come into abutmentwith` guide 89 and operate as a positive stop with openings 83 and 85cut down to a point at which the amount of iuid for maximum capacitywill not be much exceeded. This still leaves the ports 83 and 85substantially the only agency limiting the flow, the parts beingotherwise designed and apportioned to the demands of the system so thatat the widest opening, the pressure drop through the ports will still besufficient to maintain the low substantially independent of the pressureafter the iuid passes through the ports. It will be obvious that themethod above outlined could be practiced with any one of a large numberof diierent types of valves as effectively as with the valveillustrated.

In the usual thermometer bulb with the illing in the form of ageometrically solid mass, where a considerable amount of liquid iscontained in the bulb, convection currents are essential to acomparatively quick response. It is, therefore, advisable to installsuch a bulb in a horizontal position, because if it is vertical risingcurrents follow the surface of the bulb to its top without mixing withcontiguous liquid, and differences in temperature must be communicatedto the core of the liquid by conductivity only. In most liquids, andespecially in the liquids employed for this purpose, conductivity is lowand a response depending on such action is very slow.

In the thin annular chamber 26 all of the expansive liquid ispractically contiguous to the heat transmitting medium, and the responseto change in temperature is very rapid on account of the large amount ofsurface exposed compared with the volume of the bulb.

The bulb functions practically the same in any position.

Without further elaboration, the foregoing will so fully explain thegist of my invention, that others may, by applying current knowledge,readily adapt the .same for use under various conditions'of service..will, for instance, be obvious, that if either a liquid or a solidmaterial having a negative coeilicient of expansion, and' suflicientlstable in its action for thermometric wor were available, 1t would bevnecessary to change back to the ordinary form of bulb to obtain aninitial response in the same direction as the permanent response. Theseand man other modifications andalterations may rea ily be made by thoseskilled in theart without eliminating certain features which mayproperly be said to constitute the essential items of novelty involved,which items are into temperature, first over the outside and thenthrough the inside of said bulb.

2. A thermometer comprising a. bulb in the form of a tubular chamberexposed on the outside and the inside to the temperature to be measured,said chamber having an outer wall of lower expansivity and thermalcon-`y ductivity than the inner wall. y

3. A thermometer comprising a bulb in the form of a tubular chamberexposed on the outside and the inside to the temperature to.

be measured, said chamber having an `outer wall of lower expansivitythan the inner wall.

4. A thermometer' bulb comprising an innerftube of copper, an outer tubeof steel heavily nickel plated and telescoped over lsaid inner tube todefine a thin annular chamber, ringsat the ends of said tubeshermetically sealing said chamber, a sleeve hermetically sealed at itsend to the outside of said outer tube and enlarged intermediate its endsto define a storage chamber, a hermetically sealed body of variablevolume in said chamber, and external means for varying the volume ofsaid body, said outer tube havingl 'ports opening into said chamber.

5. A thermometer bulb comprising an inner tube, an outer tube telescopedover said inner tube to define a thin annular chamber, and rings at theends of said tubes hermetically sealing saidv chamber, said outer tubebeig of lower expansivity than said inner tu 6. A thermometer bulbcomprising an inner tube of copper, an outer tube of steel heavilynicldel plated and telescoped over said inner tube to define a thinannular chamber, and rings at the ends of said tubes her'- meti'callysealing said chamber.

7. A thermometer bulb comprising an inner tube of relatively thinmaterial possessin a high degree of heat conductivity and a hico-efiicient of expansion, an outer tube te scoped'over 'said'inner tubehaving a relativelfy ow co-eicient of expansion, a covering or theeutertube of relatively low thermal conductlvity compared with said innertube,

. tube, means for sealing the space between the tubes to define a thintubular chamber, and fluid within y-said chamber responsive to changesin temperature.

In witness whereof, I hereunto subscribe my name this 26th dav of J anua1925.

BYRON J. P PPER.

